Hand tremors are one of the most common movement disorders, affecting an estimated 10 million people in the U.S., with growing numbers due to the aging population. The prevalence increases with age, increasing from 5-10% of the population over 65, to above 20% over 95. Essential tremor is characterized by oscillatory movement, for example between 4-12 Hz, affecting distal limbs, like the hands. Unlike Parkinson's tremor, which exists at rest, essential tremor affects postural and kinetic activities, meaning tremor is invoked by holding a limb against gravity or during intentional movement, respectively. Tremor is also a significant problem for patients with other diseases, such as orthostatic tremor, multiple sclerosis and Parkinson's Disease. Treatment options for these conditions are limited, have undesirable side effects, or have high risk relative to the potential benefits, so alternative treatment is warranted. A number of conditions, such as tremors, can be treated through some form of transcutaneous peripheral nerve stimulation.
Designing a device to accomplish such a treatment is challenging. One difficulty in designing a product for patients with tremors is creating a device that is easy to position and configure for individuals whose hands are unsteady. People have a wide variation in wrist diameters, nerve locations, nerve depolarization characteristics, and skin conduction that leads to challenges in designing a device to comfortably, safely, and reliably target peripheral nerves for stimulation across a broad population. For instance, in a wrist-worn device targeting the median, ulnar, and radial nerves at the wrist, the band circumference for the adult population would have to vary from 13.5-19.8 cm to accommodate 5th percentile female to 95th percentile male. See Henry Dreyfus Associates, “The Measure of Man and Woman”, Wiley, 2001. In addition to differences in size, there are variations in the location, depth, and branching of nerves. Thus, a system and method that can reliably stimulate one or more nerves in the wrist across a wide range of wrist sizes would be advantageous in treating hand tremors.
A second challenge to designing such a device is that tremors vary between different people. Even within the same person tremor can occur at variable times throughout the day, depending on multiple factors, including but not limited to the patient's stress level, fatigue, and\diet. Thus, individually customized and responsive therapy capable of treating the tremor when it occurs or is likely to occur can provide a more effective, yet power efficient device.